Evaluation of the strength of shaved steamed Pinus radiata poles

Bending strength of Pinus radiata (D.Don) poles is critical in a range of structural applications, such as retaining-walls. Pinus radiata poles in a wet, shaved and steamed condition were obtained from five suppliers located across the central North Island of New Zealand. This sample of poles met the stiffness (Modulus of Elasticity) value expected of normaldensity poles according to New Zealand Standard3603, but their characteristic bending and compression stresses were 40% and 39%, respectively, lower than expected. Applying a maximum allowable knot size restriction (measured as the knot diameter ratio) made little difference to the results. Applying a minimum stress-wave velocity (measured using a HM200 device) also had little effect on the derived characteristic values until the value was raised to 3.2 km/s, which would eliminate about 20% of the sample. A minimum stress-wave velocity reading of 2.8 km/s is recommended. At this level, some poles from two of the five suppliers would have to be rejected. These results indicate that pole selection based on the basic density of outer-zone wood is less effective than that using stress-wave velocity measured using a HM-200 device. It is recommended that New Zealand Standard3603 should be amended in the light of these findings.